U.S. patent application number 12/296021 was filed with the patent office on 2009-05-28 for multiphase level shift system.
Invention is credited to Shiro Dosho, Akinori Matsumoto, Takashi Morie, Shiro Sakiyama, Yusuke Tokunaga.
Application Number | 20090134931 12/296021 |
Document ID | / |
Family ID | 39401445 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090134931 |
Kind Code |
A1 |
Sakiyama; Shiro ; et
al. |
May 28, 2009 |
MULTIPHASE LEVEL SHIFT SYSTEM
Abstract
Each of n level shifters (LS0 to LS7) includes an NMOS
transistor (Mn1) for receiving any one of n clock signals (P0 to
P7) and a PMOS transistor (Mp1) for receiving an output signal from
another level shifter. An output signal given to the PMOS
transistor (Mp1) included in each of the level shifters (LS0 to
LS7) is an output signal of the level shifter which receives the
clock signal whose phase delay amount with respect to the clock
signal given to the NMOS transistor (Mn1) included in that level
shifter is a phase amount X (0.degree.<X<180.degree.). The
phase amounts X of the n level shifters (LS0 to LS7) are equal to
each other.
Inventors: |
Sakiyama; Shiro; (Kyoto,
JP) ; Matsumoto; Akinori; (Osaka, JP) ; Morie;
Takashi; (Osaka, JP) ; Dosho; Shiro; (Osaka,
JP) ; Tokunaga; Yusuke; (Hyogo, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Family ID: |
39401445 |
Appl. No.: |
12/296021 |
Filed: |
June 15, 2007 |
PCT Filed: |
June 15, 2007 |
PCT NO: |
PCT/JP2007/062125 |
371 Date: |
October 3, 2008 |
Current U.S.
Class: |
327/333 |
Current CPC
Class: |
H03K 3/0315 20130101;
H03K 3/354 20130101; H03K 19/01855 20130101 |
Class at
Publication: |
327/333 |
International
Class: |
H03L 5/00 20060101
H03L005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2006 |
JP |
2006-312041 |
Claims
1. A multiphase level shift system for performing voltage
conversion with respect to output voltages of n clock signals (n is
an integer of three or more) having equal cycles, an interval
between phases thereof being a phase amount T (T=360.degree./n),
comprising: n level shifters in a one-to-one correspondence with
the n clock signals, wherein each of the n level shifters includes
a first NMOS transistor and a first PMOS transistor, the first NMOS
transistor included in each of the n level shifters is connected
between an output node for outputting an output signal of said
level shifter and a ground node, and a gate of the first NMOS
transistor receives the clock signal corresponding to said level
shifter, the first PMOS transistor included in each of the n level
shifters is connected between the output node and a power supply
node, and a gate of the first PMOS transistor receives an output
signal from another level shifter different from said level
shifter, the output signal given to the gate of the first PMOS
transistor included in each of the n level shifters is an output
signal of the level shifter which receives the clock signal delayed
by a phase amount X (0.degree.<X<180.degree.) from the clock
signal given to the gate of the first NMOS transistor included in
said level shifter, and the phase amounts X of the n level shifters
are equal to each other.
2. The multiphase level shift system of claim 1, wherein each of
the n level shifters further includes a delay element for delaying
an output of said level shifter, a falling delay amount in each of
the n level shifter is a phase amount LSf, and a rising delay
amount in said level shifter is a phase amount LSr, a falling delay
amount DDf in the delay element included in each of the n level
shifters is: DDf.gtoreq.180.degree.-LSf-X, and a rising delay
amount DDR in said delay element is:
DDR.ltoreq.180.degree.-LSr-X.
3. The multiphase level shift system of claim 2, wherein the
falling delay amount DDf in the delay element included in each of
the n level shifters is larger than the falling delay amount DDR of
said delay element.
4. The multiphase level shift system of claim 1, wherein a falling
edge of the output signal given to the gate of the first PMOS
transistor included in each of the n level shifters occurs
subsequent in time to or simultaneously with a falling edge of the
clock signal given to the gate of the first NMOS transistor
included in said level shifter, and a rising edge of the output
signal given to the gate of said first PMOS transistor occurs prior
in time to or simultaneously with a rising edge of said clock
signal.
5. The multiphase level shift system of claim 1, wherein each of
the n level shifters further includes a second PMOS transistor, the
second PMOS transistor included in each of the n level shifters and
the first PMOS transistor included in said level shifter are
connected in series between the power supply node and the output
node, and a gate of said second PMOS transistor receives the output
signal of another level shifter different from said level shifter,
the output signal given to the gate of the second PMOS transistor
included in each of the n level shifters is an output signal of the
level shifter corresponding to the clock signal delayed by a phase
amount Y (X<Y<360.degree.-X) from the clock signal given to
the first NMOS transistor included in said level shifter, and the
phase amounts Y of the n level shifters are equal to each
other.
6. The multiphase level shift system of claim 5, wherein a falling
edge of the output signal given to the gate of the second PMOS
transistor included in each of the n level shifters occurs
subsequent in time to or simultaneously with a falling edge of the
clock signal given to the gate of the first NMOS transistor
included in said level shifter, and a rising edge of the output
signal given to the gate of the first PMOS transistor included in
said level shifter occurs prior in time to or simultaneously with a
rising edge of said clock signal.
7. The multiphase level shift system of claim 1, wherein each of
the n level shifters further includes a second NMOS transistor, the
second NMOS transistor included in each of the n level shifters and
the first NMOS transistor included in said level shifter are
connected in series between the ground node and the output node,
and a gate of said second NMOS transistor receives a clock signal
different from the clock signal given to said first NMOS
transistor, the clock signal given to the second NMOS transistor
included in each of the n level shifters is advanced by a phase
amount Z (0.degree.<Z<180.degree.) from the clock signal
given to the gate of the first NMOS transistor included in said
level shifter, and the phase amounts Z of the n level shifters are
equal to each other.
8. The multiphase level shift system of claim 7, wherein a falling
edge of the output signal given to the gate of the first PMOS
transistor included in each of the n level shifters occurs
subsequent in time to or simultaneously with a falling edge of the
clock signal given to the gate of the second NMOS transistor
included in said level shifter, and a rising edge of the output
signal given to the gate of said first PMOS transistor occurs prior
in time to or simultaneously with a rising edge of the clock signal
given to the gate of the first NMOS transistor included in said
level shifter.
9. The multiphase level shift system of claim 1, wherein each of
the n level shifters further includes a resistance element, one end
of the resistance element included in each of the n level shifters
is connected to the output node of said level shifter, and the
other end of said resistance element is connected to the output
node of another level shifter different from said level shifter,
and the output node connected to the other end of the resistance
element included in each of the n level shifters is the output node
of the level shifter corresponding to the clock signal delayed by
the phase amount T from the clock signal corresponding to said
level shifter.
10. A multiphase level shift system for performing voltage
conversion with respect to output voltages of n clock signals (n is
an integer of three or more) having equal cycles, an interval
between phases thereof being a phase amount T (T=360.degree./n),
comprising: n level shifters in a one-to-one correspondence with
the n clock signals; and n resistance elements in a one-to-one
correspondence with the n level shifters, wherein each of the n
level shifters performs voltage conversion with respect to the
clock signal corresponding to said level shifter to generate an
output signal corresponding to said clock signal, and outputs said
output signal from an output node, one end of each of the n
resistance elements is connected to the output node of the level
shifter corresponding to said resistance element, and the other end
of said resistance element is connected to the output node of
another level shifter different from the level shifter
corresponding to said resistance element, and the output node
connected to the other end of each of the n resistance elements is
the output node of the level shifter corresponding to the clock
signal delayed by the phase amount T from the clock signal
corresponding to the level shifter connected to the one end of said
resistance element.
11. The multiphase level shift system of claim 3, wherein a falling
edge of the output signal given to the gate of the first PMOS
transistor included in each of the n level shifters occurs
subsequent in time to or simultaneously with a falling edge of the
clock signal given to the gate of the first NMOS transistor
included in said level shifter, and a rising edge of the output
signal given to the gate of said first PMOS transistor occurs prior
in time to or simultaneously with a rising edge of said clock
signal.
12. The multiphase level shift system of claim 2, wherein each of
the n level shifters further includes a resistance element, one end
of the resistance element included in each of the n level shifters
is connected to the output node of said level shifter, and the
other end of said resistance element is connected to the output
node of another level shifter different from said level shifter,
and the output node connected to the other end of the resistance
element included in each of the n level shifters is the output node
of the level shifter corresponding to the clock signal delayed by
the phase amount T from the clock signal corresponding to said
level shifter.
13. The multiphase level shift system of claim 5, wherein each of
the n level shifters further includes a resistance element, one end
of the resistance element included in each of the n level shifters
is connected to the output node of said level shifter, and the
other end of said resistance element is connected to the output
node of another level shifter different from said level shifter,
and the output node connected to the other end of the resistance
element included in each of the n level shifters is the output node
of the level shifter corresponding to the clock signal delayed by
the phase amount T from the clock signal corresponding to said
level shifter.
14. The multiphase level shift system of claim 7, wherein each of
the n level shifters further includes a resistance element, one end
of the resistance element included in each of the n level shifters
is connected to the output node of said level shifter, and the
other end of said resistance element is connected to the output
node of another level shifter different from said level shifter,
and the output node connected to the other end of the resistance
element included in each of the n level shifters is the output node
of the level shifter corresponding to the clock signal delayed by
the phase amount T from the clock signal corresponding to said
level shifter.
Description
TECHNICAL FIELD
[0001] The present invention relates to a system for performing
voltage conversion with respect to a given signal and, more
particularly, to a system for performing voltage conversion with
respect to input amplitudes of clock signals having multiple
phases.
BACKGROUND ART
[0002] Clock signals having multiple phases are used for a write
control of DVD or the like or high-speed communication (DDR, QDR,
ODR, etc.). In general, the clock signals having multiple phases
are generated using, for example, a phase locked loop (PLL)
including a phase detector (PD), a charge pump (CP), a low-pass
filter (LPF), and an oscillation circuit (a voltage controlled
oscillator (VCO), a current controlled oscillator (CCO)). For
example, clock signals P0 to P7 having eight phases as shown in
FIG. 20A or clock signals P0 to P8 having nine phases as shown in
FIG. 20B are generated. Also, the voltage level of a clock signal
generated by the oscillation circuit is typically lower than the
voltage level of a power supply, and therefore, a level shifter for
converting the voltage level of the clock signal into the voltage
level of the power supply is required.
[0003] FIG. 21A shows a configuration of a general level shifter.
In the general level shifter LS90, the gate of an NMOS transistor
Mn8 receives a clock signal P(+), and the gate of an NMOS
transistor Mn9 receives a clock signal P(-). The phase difference
between the clock signal P(+) and the clock signal P(-) is
180.degree.. Also, the gate of a PMOS transistor Mp8 receives a
voltage (output signal Q(-)) at a connection point of the
transistors Mn9 and a transistor Mp9, and the gate of the PMOS
transistor Mp9 receives a voltage (output signal Q(+)) at a
connection point of the transistors Mn8 and Mp8. The output signal
Q(+) corresponds to the clock signal P(+), and the output signal
Q(-) corresponds to the clock signal P(-).
[0004] FIG. 21B is a waveform diagram for describing an operation
of the level shifter LS90 of FIG. 21A. In the level shifter LS90,
when the clock signal P(+) rises, the voltage value of the output
signal Q(+) starts decreasing, and when the output signal Q(+)
becomes lower than or equal to a threshold voltage .DELTA.Vt, the
voltage value of the output signal Q(-) starts increasing. Also,
when the clock signal P(-) rises, the voltage value of the output
signal Q(-) starts decreasing, and when the output signal Q(-)
becomes lower than or equal to the threshold voltage .DELTA.Vt, the
voltage value of the output signal Q(+) starts increasing.
[0005] Here, attention is paid to the NMOS transistor Mn8 and the
PMOS transistor Mp8. A drive period Ton(n) of the NMOS transistor
Mn8 is a period from a rising edge to a falling edge of the clock
signal P(+), and a drive period of the PMOS transistor Mp8 is a
period from a falling edge to a rising edge of the output signal
Q(-).
[0006] (Voltage Conversion of Clock Signals Having Even Number of
Phases)
[0007] When voltage conversion is performed with respect to the
clock signals P0 to P7 having eight phases (even number of phases),
since there are four pairs of clock signals having a phase
difference of 180.degree., four level shifters LS90a are required
as shown in FIG. 22. Specifically, the four level shifters LS90a
each receive any one of the clock signals P0 to P3 as the clock
signal P(+), and one of the clock signals P4 to P7 that has a phase
difference of 180.degree. with respect to the clock signal P(+), as
the clock signal P(-). Thereby, output signals Q0 to Q7
corresponding to the clock signals P0 to P7 are output.
[0008] (Voltage Conversion of Clock Signals Having Odd Number of
Phases)
[0009] On the other hand, when voltage conversion is performed with
respect to the clock signals P0 to P8 having nine phases (odd
number of phases), since there are no clock signals having a phase
difference of 180.degree., inverted clock signals (-P0) to (-P8) as
shown in FIG. 23B having nine phases which have a phase difference
of 180.degree. with respect to the respective clock signals having
nine phases need to be generated using a phase conversion circuit
as shown in FIG. 23A. In this case, as shown in FIG. 24, nine level
shifters LS90b are required. Specifically, the nine level shifters
LS90b each receive any one of the clock signals P0 to P8 as the
clock signal P(+), and an inverted clock signal having a phase
difference of 180.degree. with respect to the clock signal P(+), as
the clock signal P(-). Thereby, output signals Q0 to Q8
corresponding to the clock signals P0 to P8 are output.
Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2000-307397
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0010] However, in conventional level shifters, an ON period
(current extraction period) of the NMOS transistor Mn8 and an ON
period (current supply period) of the PMOS transistor Mp8 overlap
each other, so that a through current from a power supply node to a
ground node occurs, leading to an increase in power consumption.
The overlapping of the ON periods of both the transistors also
equivalently reduces the drive ability when the NMOS transistor Mn8
is in the ON state, so that the through rate of falling of the
voltage value of the output signal is deteriorated, resulting in a
deterioration in phase precision of the output signal.
[0011] An object of the present invention is to suppress the
occurrence of a through current in a level shifter.
Solution to the Problems
[0012] According to the present invention, a multiphase level shift
system is provided for performing voltage conversion with respect
to output voltages of n clock signals (n is an integer of three or
more) having equal cycles, an interval between phases thereof being
a phase amount T (T=360.degree./n). The system includes n level
shifters in a one-to-one correspondence with the n clock signals.
The each of the n level shifters includes a first NMOS transistor
and a first PMOS transistor. The first NMOS transistor included in
each of the n level shifters is connected between an output node
for outputting an output signal of said level shifter and a ground
node, and a gate of the first NMOS transistor receives the clock
signal corresponding to said level shifter. The first PMOS
transistor included in each of the n level shifters is connected
between the output node and a power supply node, and a gate of the
first PMOS transistor receives an output signal from another level
shifter different from said level shifter. The output signal given
to the gate of the first PMOS transistor included in each of the n
level shifters is an output signal of the level shifter which
receives the clock signal delayed by a phase amount X
(0.degree.<X<180.degree.) from the clock signal given to the
gate of the first NMOS transistor included in said level shifter.
The phase amounts X of the n level shifters are equal to each
other.
[0013] In the multiphase level shift system, the overlapping of a
period during which a current is extracted from the output node to
the ground node (current extraction period) and a period during
which a current flows from the power supply node to the output node
(current supply period) can be eliminated. Thereby, the occurrence
of a through current in each level shifter can be suppressed, so
that power consumption can be reduced. Also, the phase precision of
the output signal with respect to the clock signal can be
improved.
[0014] Also, each of the n level shifters further includes a delay
element for delaying an output of said level shifter. A falling
delay amount in each of the n level shifter is a phase amount LSf,
and a rising delay amount in said level shifter is a phase amount
LSr. A falling delay amount DDf in the delay element included in
each of the n level shifters is (DDf.gtoreq.180.degree.-LSf-X), and
a rising delay amount DDR in said delay element is
(DDR.ltoreq.180.degree.-LSr-X).
[0015] In the multiphase level shift system, the occurrence of a
through current can be suppressed by adjusting a delay amount in
the delay element. Therefore, the multiphase level shift system can
be easily constructed without changing the design of the level
shifter.
[0016] Preferably, the falling delay amount DDf in the delay
element included in each of the n level shifters is larger than the
falling delay amount DDR of said delay element.
[0017] In the multiphase level shift system, the possible range of
the phase amount X is broadened, so that the multiphase level shift
system capable of suppressing the occurrence of a through current
can be easily constructed.
[0018] Preferably, a falling edge of the output signal given to the
gate of the first PMOS transistor included in each of the n level
shifters occurs subsequent in time to or simultaneously with a
falling edge of the clock signal given to the gate of the first
NMOS transistor included in said level shifter, and a rising edge
of the output signal given to the gate of said first PMOS
transistor occurs prior in time to or simultaneously with a rising
edge of said clock signal.
[0019] In the multiphase level shift system, the first PMOS
transistor goes into the non-drive state when a rising edge of the
output signal occurs, and goes into the drive state when a falling
edge of the output signal occurs. Also, the first NMOS transistor
goes into the drive state when a rising edge of the clock signal
occurs, and goes into the non-drive state when a falling edge of
the clock signal occurs. In other words, the first NMOS transistor
goes into the non-drive state before (or at the same time) the
first PMOS transistor goes into the drive state, and the first PMOS
transistor goes into the non-drive state before (or at the same
time) the first NMOS transistor goes into the drive state.
[0020] Also, each of the n level shifters further includes a second
PMOS transistor. The second PMOS transistor included in each of the
n level shifters and the first PMOS transistor included in said
level shifter are connected in series between the power supply node
and the output node, and a gate of said second PMOS transistor
receives the output signal of another level shifter different from
said level shifter. The output signal given to the gate of the
second PMOS transistor included in each of the n level shifters is
an output signal of the level shifter corresponding to the clock
signal delayed by a phase amount Y (X<Y<360.degree.-X) from
the clock signal given to the first NMOS transistor included in
said level shifter. The phase amounts Y of the n level shifters are
equal to each other.
[0021] In the multiphase level shift system, when both the first
and second PMOS transistors go into the drive state, a current is
supplied from a power supply node to the output node. In other
words, a period during which both the first and second PMOS
transistors are in the drive state is a current supply period.
Also, the overlapping of the current extraction period and the
current supply period can be eliminated, so that the occurrence of
a through current can be suppressed in each level shifter. Further,
the duty ratio of the output signal can be adjusted by adjusting
the phase amount Y.
[0022] Preferably, a falling edge of the output signal given to the
gate of the second PMOS transistor included in each of the n level
shifters occurs subsequent in time to or simultaneously with a
falling edge of the clock signal given to the gate of the first
NMOS transistor included in said level shifter, and a rising edge
of the output signal given to the gate of the first PMOS transistor
included in said level shifter occurs prior in time to or
simultaneously with a rising edge of said clock signal.
[0023] In the multiphase level shift system, the second PMOS
transistor goes into the drive state when a falling edge of the
output signal occurs, and goes into the non-drive state when a
rising edge of the output signal occurs. Also, the first NMOS
transistor goes into the non-drive state before (or at the same
time) both the first and second PMOS transistors goes into the
drive state, and at least one of the first and second PMOS
transistors goes into the non-drive state before (or at the same
time) the first NMOS transistor goes into the drive state.
[0024] Also, each of the n level shifters further includes a second
NMOS transistor. The second NMOS transistor included in each of the
n level shifters and the first NMOS transistor included in said
level shifter are connected in series between the ground node and
the output node, and a gate of said second NMOS transistor receives
another clock signal different from the clock signal given to said
first NMOS transistor. The clock signal given to the second NMOS
transistor included in each of the n level shifters is advanced by
a phase amount Z (0.degree.<Z<180.degree.) from the clock
signal given to the gate of the first NMOS transistor included in
said level shifter. The phase amounts Z of the n level shifters are
equal to each other.
[0025] In the multiphase level shift system, when both the first
and second NMOS transistors go into the drive state, a current is
extracted from the output node to the ground node. In other words,
a period during which both the first and second NMOS transistors
are in the drive state is the current extraction period. Also, the
overlapping of the current extraction period and the current supply
period can be eliminated, so that the occurrence of a through
current can be suppressed.
[0026] Preferably, a falling edge of the output signal given to the
gate of the first PMOS transistor included in each of the n level
shifters occurs subsequent in time to or simultaneously with a
falling edge of the clock signal given to the gate of the second
NMOS transistor included in said level shifter, and a rising edge
of the output signal given to the gate of said first PMOS
transistor occurs prior in time to or simultaneously with a rising
edge of the clock signal given to the gate of the first NMOS
transistor included in said level shifter.
[0027] In the multiphase level shift system, the second NMOS
transistor goes into the drive state when a rising edge of the
clock signal occurs, and goes into the non-drive state when a
falling edge of the clock signal occurs. Also, at least one of the
first and second PMOS transistors goes into the non-drive state
before (or at the same time) the first PMOS transistor goes into
the drive state, and the first PMOS transistor goes into the
non-drive state before (or at the same time) both the first and
second NMOS transistors go into the drive state.
[0028] Also, each of the n level shifters further includes a
resistance element. One end of the resistance element included in
each of the n level shifters is connected to the output node of
said level shifter, and the other end of said resistance element is
connected to the output node of another level shifter different
from said level shifter. The output node connected to the other end
of the resistance element included in each of the n level shifters
is the output node of the level shifter corresponding to the clock
signal delayed by the phase amount T from the clock signal
corresponding to said level shifter.
[0029] In the multiphase level shift system, a phase variation of
the output signal in each level shifter is interpolated using
adjacent phases, so that the phase precision of the output signal
can be further improved.
[0030] Also, a multiphase level shift system includes n level
shifters in a one-to-one correspondence with the n clock signals,
and n resistance elements in a one-to-one correspondence with the n
level shifters. Each of the n level shifters performs voltage
conversion with respect to the clock signal corresponding to said
level shifter to generate an output signal corresponding to said
clock signal, and outputs said output signal from an output node.
One end of each of the n resistance elements is connected to the
output node of the level shifter corresponding to said resistance
element, and the other end of said resistance element is connected
to the output node of another level shifter different from the
level shifter corresponding to said resistance element. The output
node connected to the other end of each of the n resistance
elements is the output node of the level shifter corresponding to
the clock signal delayed by the phase amount T from the clock
signal corresponding to the level shifter connected to the one end
of said resistance element.
[0031] In the multiphase level shift system, a phase variation of
the output signal in each level shifter is interpolated using
adjacent phases, so that the phase precision of the output signal
can be further improved.
EFFECT OF THE INVENTION
[0032] As described above, the occurrence of a through current can
be suppressed in each level shifter, so that power consumption can
be reduced. Also, the phase precision of the output signal with
respect to the clock signal can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a circuit diagram showing an exemplary
configuration of a multiphase level shift system according to a
first embodiment of the present invention.
[0034] FIG. 2 is a conceptual diagram showing a phase relationship
between a clock signal given to each level shifter of FIG. 1, and
an output signal.
[0035] FIG. 3 is a signal waveform diagram for describing an
operation of the multiphase level shift system of FIG. 1.
[0036] FIG. 4A is a schematic diagram for describing
non-overlapping conditions in the multiphase level shift system of
the first embodiment. FIG. 4B is a waveform diagram showing a phase
relationship between a clock signal and an output signal when the
non-overlapping conditions are satisfied.
[0037] FIG. 5 is a circuit diagram showing an exemplary
configuration of a multiphase level shift system according to a
second embodiment of the present invention.
[0038] FIG. 6A is a circuit diagram showing an exemplary internal
configuration of a delay element of FIG. 5. FIG. 6B is a waveform
diagram for describing an operation in the delay element of FIG.
6A.
[0039] FIG. 7 is a signal waveform diagram for describing an
operation of the multiphase level shift system of FIG. 5.
[0040] FIG. 8A is a schematic diagram for describing
non-overlapping conditions in the multiphase level shift system of
the second embodiment. FIG. 8B is a waveform diagram showing a
phase relationship between a clock signal and an output signal when
the non-overlapping conditions are satisfied.
[0041] FIG. 9 is a circuit diagram showing an exemplary
configuration of a multiphase level shift system according to a
third embodiment of the present invention.
[0042] FIG. 10 is a conceptual diagram showing a phase relationship
between a clock signal given to each level shifter of FIG. 9, and
an output signal.
[0043] FIG. 11 is a signal waveform diagram for describing an
operation of the multiphase level shift system of FIG. 9.
[0044] FIG. 12A is a schematic diagram for describing
non-overlapping conditions in the multiphase level shift system of
the third embodiment. FIG. 12B is a waveform diagram showing a
phase relationship between a clock signal and an output signal when
the non-overlapping conditions are satisfied.
[0045] FIG. 13 is a circuit diagram showing an exemplary
configuration of a multiphase level shift system according to a
fourth embodiment of the present invention.
[0046] FIG. 14 is a conceptual diagram showing a phase relationship
between a clock signal given to each level shifter of FIG. 13, and
an output signal.
[0047] FIG. 15 is a signal waveform diagram for describing an
operation of the multiphase level shift system of FIG. 13.
[0048] FIG. 16A is a schematic diagram for describing
non-overlapping conditions in the multiphase level shift system of
the fourth embodiment. FIG. 16B is a waveform diagram showing a
phase relationship between a clock signal and an output signal when
the non-overlapping conditions are satisfied.
[0049] FIG. 17 is a circuit diagram showing an exemplary
configuration of a multiphase level shift system according to a
fifth embodiment of the present invention.
[0050] FIG. 18 is a conceptual diagram for describing a resistor
network constructed between level shifters of FIG. 17.
[0051] FIG. 19 is a circuit diagram showing a variation of the
multiphase level shift system of the fifth embodiment of the
present invention.
[0052] FIG. 20A is a waveform diagram showing clock signals having
eight phases. FIG. 20B is a waveform diagram showing clock signals
having nine phases.
[0053] FIG. 21A is a circuit diagram showing a configuration of a
conventional level shifter. FIG. 21B is a waveform diagram for
describing an operation of a level shifter of FIG. 21A.
[0054] FIG. 22 is a diagram showing a set of level shifters for
performing voltage conversion with respect to clock signals having
eight phases.
[0055] FIG. 23A is a circuit diagram showing a generation circuit
for generating inverted clock signals. FIG. 23B is a waveform
diagram showing inverted clock signals corresponding to clock
signals having nine phases.
[0056] FIG. 24 is a diagram showing a set of level shifters for
performing voltage conversion with respect to clock signals having
nine phases.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0057] LS0 to LS7, LS50 to LS57 level shifter [0058] Mn1 NMOS
transistor (first NMOS transistor) [0059] Mp1 PMOS transistor
(first PMOS transistor) [0060] DD delay element [0061] Mp2 PMOS
transistor (second PMOS transistor) [0062] Mn2 NMOS transistor
(second NMOS transistor) [0063] RR, RR1 to RR7 resistance
element
BEST MODE FOR CARRYING OUT THE INVENTION
[0064] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying drawings.
Note that the same or like parts are indicated by the same
reference numerals and will not be repeatedly described.
First Embodiment
[0065] <Multiphase Level Shift System>
[0066] FIG. 1 shows a whole configuration of a multiphase level
shift system according to a first embodiment of the present
invention. The multiphase level shift system performs voltage
conversion with respect to output amplitudes of n clock signals (n
is an integer of three or more) to output n output signals
corresponding to the respective n clock signals. In other words, a
phase relationship between the n output signals corresponds to a
phase relationship between the n clock signals. The n clock signals
have a phase interval T of 360.degree./n. This system includes n
level shifters in a one-to-one correspondence with the n clock
signals. Note that a case where "n=8" is shown in FIG. 1. The clock
signals P0 to P7 have the following phases.
TABLE-US-00001 Clock signal P0: zeroth phase (0.degree.) Clock
signal P1: first phase (45.degree.) Clock signal P2: second phase
(90.degree.) Clock signal P3: third phase (135.degree.) Clock
signal P4: fourth phase (180.degree.) Clock signal P5: fifth phase
(225.degree.) Clock signal P6: sixth phase (270.degree.) Clock
signal P7: seventh phase (315.degree.)
[0067] <Configuration of Level Shifters>
[0068] The level shifters LS0 to LS7 each include an NMOS
transistor Mn1 and a PMOS transistor Mp1. The source of the NMOS
transistor Mn1 is connected to a ground node which receives a
ground potential VSS, the source of the PMOS transistor Mp1 is
connected to a power supply node which receives a power supply
potential VDD, and the drains of the NMOS transistor Mn1 and the
PMOS transistor Mp1 are connected to each other. A voltage at a
connection point (output node) of the NMOS transistor Mn1 and the
PMOS transistor Mp1 is output as an output signal of the level
shifter.
[0069] In each of the level shifters LS0 to LS7, the gate of the
NMOS transistor Mn1 receives a clock signal corresponding to the
level shifter. On the other hand, the gate of the PMOS transistor
Mp1 receives an output signal of a level shifter corresponding to a
clock signal delayed by a phase amount X
(0.degree.<X<180.degree.) from the clock signal given to the
NMOS transistor Mn1. Also, the level shifters all have the same
phase amount X. Note that X=135.degree. in FIG. 1.
[0070] <Phase Amount X in Each Level Shifter>
[0071] FIG. 2 shows a phase relationship between a clock signal
given to the NMOS transistor Mn1 and an output signal given to the
PMOS transistor Mp1 in each of the level shifters LS0 to LS7 of
FIG. 1.
[0072] In a level shifter LS.sub.(k) corresponding to a clock
signal P.sub.(k) having a k.sup.th phase, the NMOS transistor Mn1
receives the clock signal P.sub.(k), and the PMOS transistor Mp1
receives an output signal Q.sub.(k+.alpha.) from a level shifter
LS.sub.(k+.alpha.) corresponding to a clock signal
P.sub.(k+.alpha.). The clock signal P.sub.(k+.alpha.) is delayed by
the phase amount X from the clock signal P.sub.(k). Here, "k" is an
integer of zero or more and 0.ltoreq.k.ltoreq.n-1, and ".alpha." is
an integer and .alpha.=X/T (T is a phase interval of clock
signals). Note that, when (k+.alpha.)>(n-1), (k+.alpha.) is a
remainder which is left when (k+.alpha.) is divided by n. In FIG.
2, n=8, and .alpha.=135.degree./45.degree.=3.
[0073] <Operation>
[0074] Next, an operation of the multiphase level shift system of
FIG. 1 will be described with reference to FIG. 3. Note that, here,
the PMOS transistor goes into a drive state (i.e., a state in which
a current flows from the power supply node via the PMOS transistor
to the output node) when the output signal becomes lower than or
equal to a threshold voltage .DELTA.Vt of the PMOS transistor Mp1,
and a non-drive state (i.e., a state in which a drain current does
not occur in the PMOS transistor) when the output signal becomes
higher than or equal to the threshold voltage .DELTA.Vt.
[0075] Also, a rising delay amount and a falling delay amount of
each level shifter is assumed to be a phase amount "45.degree.".
The rising delay amount in a level shifter means a delay amount
from the start of rising of the voltage value of the output signal
until the output signal reaches the threshold voltage .DELTA.Vt
(i.e., the PMOS transistor goes into the drive state). The falling
delay amount in a level shifter means a delay amount from the start
of falling of the voltage value of the output signal until the
output signal reaches the threshold voltage .DELTA.Vt (i.e., the
PMOS transistor goes into the non-drive state). For the sake of
simplicity, it is assumed that the level shifters all have the same
rising delay amount and the same falling delay amount.
[0076] (Starting of Driving of NMOS Transistor)
[0077] At time t1, in the level shifter LS0, the clock signal P0
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q1 of the level
shifter LS0 starts decreasing. Also, since the output signal Q3 to
the level shifter LS0 is higher than the threshold voltage
.DELTA.Vt, the PMOS transistor Mp1 is in the non-drive state.
[0078] (Decrease in Voltage of Output Signal Q3)
[0079] At time t2, in the level shifter LS3, the clock signal P3
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q3 starts
decreasing.
[0080] (Stopping of Driving of NMOS Transistor/Starting of Driving
of PMOS Transistor)
[0081] At time t3, in the level shifter LS0, the clock signal P0
falls, so that the NMOS transistor Mn1 goes into the non-drive
state. On the other hand, the output signal Q3 becomes lower than
or equal to the threshold voltage .DELTA.Vt, so that the PMOS
transistor Mp1 goes into the drive state. Thereby, the voltage
value of the output signal Q0 starts increasing.
[0082] (Increase in Voltage of Output Signal Q6)
[0083] At time t4, in the level shifter LS6, the clock signal P6
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q6 starts
decreasing.
[0084] (Increase in Voltage of Output Signal Q3)
[0085] At time t5, in the level shifter LS3, the output signal Q6
becomes lower than or equal to the threshold voltage .DELTA.Vt, so
that the PMOS transistor Mp1 goes into the drive state. Thereby,
the voltage value of the output signal Q3 starts increasing.
[0086] (Stopping of Driving of PMOS Transistor/Starting of Driving
of NMOS Transistor)
[0087] At time t6, in the level shifter LS0, the output signal Q3
becomes higher than or equal to the threshold voltage .DELTA.Vt, so
that the PMOS transistor Mp1 goes into the non-drive state. On the
other hand, the clock signal P0 rises, so that the NMOS transistor
Mn1 goes into the drive state. Thereby, the voltage value of the
output signal Q0 starts decreasing.
[0088] Thus, in each of the level shifters LS0 to LS7, the PMOS
transistor Mp1 goes into the drive state, and at the same time, the
NMOS transistor Mn1 goes into the non-drive state, and the NMOS
transistor Mn1 goes into the drive state, and the same time, the
PMOS transistor Mp1 goes into the non-drive state. In other words,
a drive period Ton(n) of the NMOS transistor Mn1 and a drive period
Ton(p) of the PMOS transistor Mp1 do not overlap each other.
[0089] <Non-Overlapping Conditions>
[0090] Here, with reference to FIG. 4, conditions under which, in
each level shifter of this embodiment, current extraction from the
output node to the ground node is stopped before (or at the same
time) current supply from the power supply node to the output node
is started, and current extraction from the output node to the
ground node is started after (or at the same time) current supply
from the power supply node to the output node is stopped (i.e.,
conditions under which the current extraction period and the
current supply period do not substantially overlap each other:
non-overlapping conditions), will be described. Here, the level
shifters LS.sub.(k), LS.sub.(k+.alpha.), and LS.sub.(k+2.alpha.)
will be described as an example.
[0091] Note that, in the following description, the rising delay
amount and the falling delay amount in each level shifter are
considered as "phase amounts", but not "time amounts". Also, a
rising edge of the clock signal P.sub.(k) (an initial phase of the
clock signal P.sub.(k)) is assumed as a phase reference point
(0.degree.), while rising edges of the other clock signals (initial
phases of the other clock signals) and a rising edge and a falling
edge of the output signal are each represented by a phase amount
from the rising edge of the clock signal P.sub.(k).
[0092] Firstly, symbols used in the drawings and the following
expressions will be described.
[0093] <<Clock Signals>>
[0094] P.sub.(k): a clock signal having a k.sup.th phase
[0095] P.sub.(k+.alpha.): a clock signal having a
(k+.alpha.).sup.th phase
[0096] P.sub.(k+2.alpha.): a clock signal having a
(k+2.alpha.).sup.th phase
[0097] <<Output Signals>>
[0098] Q.sub.(k+.alpha.): an output signal of the level shifter
LS.sub.(k+.alpha.)
[0099] Q.sub.(k+2.alpha.): an output signal of the level shifter
LS.sub.(k+2.alpha.)
[0100] <<Delay Amounts>>
[0101] D.sub.(LS.uparw.): a rising delay amount in each level
shifter
[0102] D.sub.(LS.dwnarw.): a falling delay amount in each level
shifter
[0103] D.sub.(LS.uparw.)>0.degree.,
D.sub.(LS.dwnarw.)>0.degree.
[0104] <<Signal Edges>>
[0105] .uparw.: a rising edge of a signal
[0106] .dwnarw.: a falling edge of a signal
[0107] <<Phase Relationships>>
P.sub.(k).uparw.<P.sub.(k+.alpha.).uparw.<P.sub.(k+2.alpha.).uparw-
.<(P.sub.(k).uparw.+360.degree.)
P.sub.(k).dwnarw.=P.sub.(k).uparw.+180.degree.
[0108] <<Phase Amount X>>
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.=P.sub.(k+2.alpha.).uparw.-P.su-
b.(k+.alpha.).uparw.=X
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw.=2(P.sub.(k+.alpha.).uparw.-P.-
sub.(k).uparw.)=2X
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.>0.degree.X>0.degree.
[0109] The phase amount X which is the phase delay amount of the
clock signal P.sub.(k+.alpha.) with respect to the clock signal
P.sub.(k) is defined as in the above-described expression. Also,
the phase delay amount of the clock signal P.sub.(k+2.alpha.) with
respect to the clock signal P.sub.(k+.alpha.) is equal to the phase
delay amount of the clock signal P.sub.(k+.alpha.) with respect to
the clock signal P.sub.(k).
[0110] (Drive Period of Transistor)
[0111] In the level shifter LS.sub.(k), during a period from the
rising edge P.sub.(k).uparw. to the falling edge P.sub.(k).dwnarw.
of the clock signal P.sub.(k), the clock signal P.sub.(k) is at a
high level (e.g., higher than or equal to the threshold voltage of
the NMOS transistor Mn1), so that the NMOS transistor Mn1 is in the
drive state, and therefore, a current is extracted from the output
node to the ground node.
[0112] Also, during a period from the falling edge
Q.sub.(k+.alpha.).dwnarw. to the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.),
the clock signal Q.sub.(k+.alpha.) is lower than or equal to the
threshold voltage .DELTA.Vt of the PMOS transistor Mp1, so that the
PMOS transistor Mp1 is in the drive state, and therefore, a current
is supplied from the power supply node to the output node.
[0113] Therefore, in order to satisfy the non-overlapping
conditions, the following expressions [Expression 1-1] and
[Expression 1-2] need to be satisfied.
P.sub.(k).dwnarw..ltoreq.Q.sub.(k+.alpha.).dwnarw. [Expression
1-1]
Q.sub.(k+.alpha.).uparw..ltoreq.P.sub.(k).uparw.+360.degree.
[Expression 1-2]
[0114] Specifically, the falling edge Q.sub.(k+.alpha.).dwnarw. of
the output signal Q.sub.(k+.alpha.) occurs subsequent in time to
(or simultaneously with) the falling edge P.sub.(k).dwnarw. of the
clock signal P.sub.(k), and the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.)
occurs prior in time to (or simultaneously with) the rising edge of
the clock signal P.sub.(k).
[0115] (Timing of Occurrence of Edge of Output Signal)
[0116] In the level shifter LS.sub.(k+.alpha.), when the rising
edge P.sub.(k+.alpha.).uparw. of the clock signal P.sub.(k+.alpha.)
occurs, the voltage value of the output signal Q.sub.(k+.alpha.)
starts decreasing. Also, when the falling edge
Q.sub.(k+2.alpha.).dwnarw. of the output signal occurs, the voltage
value of the output signal Q.sub.(k+.alpha.) starts increasing.
Further, in the level shifter LS.sub.(k+2.alpha.), when the rising
edge P.sub.(k+2.alpha.).uparw. of the clock signal
P.sub.(k+2.alpha.) occurs, the voltage value of the output signal
Q.sub.(k+2.alpha.) starts decreasing.
[0117] Here, taking into consideration the falling delay amount and
the rising delay amount in each level shifter, the rising edge
Q.sub.(k+.alpha.).uparw. and the falling edge
Q.sub.(k+.alpha.).dwnarw. of the output signal Q.sub.(k+.alpha.)
are represented by [Expression 1-3] and [Expression 1-4].
Q.sub.(k+.alpha.).dwnarw.=P.sub.(k+.alpha.).uparw.+D.sub.(LS.dwnarw.)
[Expression 1-3]
Q.sub.(k+.alpha.).uparw.=Q.sub.(k+2.alpha.).dwnarw.+D.sub.(LS.uparw.)=P.-
sub.(k+2.alpha.).uparw.+D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.)
[Expression 1-4]
[0118] Specifically, the falling edge Q.sub.(k+.alpha.).dwnarw. of
the output signal Q.sub.(k+.alpha.) depends on the timing of
occurrence of the rising edge P.sub.(k+.alpha.).uparw. of the clock
signal P.sub.(k+.alpha.), and the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.)
depends on the timing of occurrence of the rising edge
P.sub.(k+2.alpha.).uparw. of the clock signal
P.sub.(k+2.alpha.).
[0119] (Phase Amount X)
[0120] (1) Initially, a lower limit value of the phase amount X is
obtained. Here, [Expression 1-3] is substituted into [Expression
1-1].
[0121] Also, since P.sub.(k).dwnarw.=P.sub.(k).uparw.+180.degree.
and P.sub.(k+2.alpha.).uparw.-P.sub.(k+.alpha.).uparw.=X,
[Expression
1-1]=P.sub.(k).uparw.+180.degree..ltoreq.P.sub.(k+.alpha.).uparw.+D.sub.(-
LS.dwnarw.)
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw..gtoreq.180.degree.-D.sub.(LS.d-
wnarw.)
X.gtoreq.180.degree.-D.sub.(LS.dwnarw.) [Expression 1-5]
[0122] Thus, [Expression 1-5] is obtained.
[0123] (2) Next, an upper limit value of the phase amount X is
obtained. Here, [Expression 1-4] is substituted into [Expression
1-2]. Also, since
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw.=2X,
[Expression
1-2]P.sub.(k+2.alpha.).uparw.+D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.).ltoreq-
.P.sub.(k).uparw.+360.degree.
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw..ltoreq.360.degree.-D.sub.(LS.-
dwnarw.)-D.sub.(LS.uparw.)
2X.ltoreq.360.degree.-D.sub.(LS.dwnarw.)-D.sub.(LS.uparw.)
[Expression 1-6]
[0124] Thus, [Expression 1-6] is obtained.
[0125] (3) Next, the range of the phase amount X is obtained.
[0126] Here, according to [Expression 1-5] and [Expression
1-6],
180.degree.-D.sub.(LS.dwnarw.).ltoreq.X.ltoreq.180.degree.-(1/2)(D.sub.(-
LS.dwnarw.)+D.sub.(LS.uparw.)) [Expression 1-7]
[0127] Also, since D.sub.(LS.dwnarw.)>0.degree.,
D.sub.(LS.uparw.)>0.degree., and X>0.degree.,
0.degree.<X<180.degree. [Expression 1-8]
[0128] Thus, [Expression 1-7] and [Expression 1-8] are
obtained.
[0129] (4) As described above, if the phase amount X satisfies
[Expression 1-7], the non-overlapping conditions can be satisfied.
Also, the possible range of the phase amount X is represented by
[Expression 1-8]. Specifically, although the possible range of the
phase amount X varies depending on the falling delay amount and the
rising delay amount of each level shifter, the phase amount X which
can satisfies the non-overlapping conditions falls within the range
represented by [Expression 1-8].
[0130] (Phase Delay Amounts D.sub.(LS.dwnarw.) and
D.sub.(LS.uparw.) in Level Shifter)
[0131] Next, the falling delay amount (D.sub.(LS.dwnarw.)) and the
rising delay amount (D.sub.(LS.uparw.)) of a level shifter are
obtained.
[Expression 1-5]D.sub.(LS.dwnarw.).gtoreq.180.degree.-X [Expression
1-9]
[Expression
1-6]D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.).ltoreq.360.degree.-2X
[Expression 1-10]
[0132] By [Expression 1-9]-[Expression 1-10],
D.sub.(LS.uparw.).ltoreq.180.degree.-X [Expression 1-11]
[0133] As described above, if the delay amount (D.sub.(LS.dwnarw.))
during signal falling in the level shifter satisfies [Expression
1-9], and the delay amount (D.sub.(LS.uparw.)) during signal rising
in the level shifter satisfies [Expression 1-11], the level shifter
can satisfy the non-overlapping conditions.
[0134] <Effect>
[0135] As described above, in each level shifter, current
extraction from the output node can be stopped before (or at the
same time) current supply to the output node is started, and
current extraction from the output node can be started after (or at
the same time) current supply to the output node is stopped (i.e.,
the overlapping of the current extraction period and the current
supply period can be eliminated). Therefore, the occurrence of a
through current flowing from the power supply node via the PMOS
transistor and the NMOS transistor to the ground node can be
suppressed. Thereby, power consumption of each level shifter can be
reduced.
[0136] Also, since the current extraction period and the current
supply period do not subsequently overlap, so that signal rising
and falling are performed with high speed in each level shifter. In
other words, the delay amount in each level shifter can be reduced.
Thereby, the phase precision of the output signal with respect to
the clock signal can be improved.
[0137] Note that the falling delay amount is preferably larger than
the rising delay amount in a level shifter. In this case, the
possible range of the phase amount X is broadened, so that the
multiphase level shift system can be easily constructed.
Second Embodiment
[0138] <Whole Configuration>
[0139] FIG. 5 shows a whole configuration of a multiphase level
shift system according to a second embodiment of the present
invention. In this system, level shifters LS0 to LS7 each further
include a delay element DD in addition to the PMOS transistor Mp1
and the NMOS transistor Mn1 of FIG. 1. The delay element DD delays
an output signal from a connection point (output node) of the NMOS
transistor Mn1 and the PMOS transistor Mp1, and outputs the
resultant signal as a delayed output signal. Also, a rising delay
amount in the delay element DD and a falling delay amount in the
delay element DD are different from each other.
[0140] <Internal Configuration of Delay Element>
[0141] FIG. 6A shows an exemplary internal configuration of the
delay element DD of FIG. 5. The delay element DD includes PMOS
transistors Dp1 and Dp2 and NMOS transistors Dn1 and Dn2. The
transistors Dp1 and Dn1 are connected in series between a power
supply node and a ground node, and the gate of each transistor
receives a voltage (an output signal from an output node) Qin at a
connection point of the transistors Mn1 and Mp1. The transistors
Dp2 and Dn2 are connected in series between the power supply node
and the ground node, and the gate of each transistor receives an
intermediate output signal Qm from a connection point of the
transistors Dp1 and Dn1. A voltage at a connection point between
the transistors Dp2 and Dn2 is output as a delayed output signal
Qout. Also, the drive ability of the PMOS transistor Dp1 is smaller
than the drive ability of the NMOS transistor Dn1. On the other
hand, the drive ability of the PMOS transistor Dp2 and the drive
ability of the NMOS transistor Dn2 are assumed to be equal to each
other.
[0142] FIG. 6B shows signal waveforms of the output signal Qin, the
intermediate output signal Qm, and the delayed output signal Qout
in the delay element DD of FIG. 6A. Since the drive ability of the
PMOS transistor Dp1 is smaller than the drive ability of the NMOS
transistor Dn1, the rising rate of the intermediate output signal
Qm is slower than the falling rate of the intermediate output
signal Qm. Thereby, the delay amount of a falling edge of the
delayed output signal Qout with respect to a falling edge of the
output signal Qin is larger than the delay amount of a rising edge
of the delayed output signal Qout with respect to a rising edge of
the output signal Qin. In other words, the falling delay amount in
the delay element DD is larger than the rising delay amount in the
delay element DD. For example, the rising delay amount in the delay
element DD is "T/2", and the falling delay amount in the delay
element DD is "T".
[0143] <Operation>
[0144] Next, an operation of the multiphase level shift system of
FIG. 5 will be described with reference to FIG. 7. It is here
assumed that the falling delay amount of the delay element DD is
"T=45.degree.", and the rising delay amount of the delay element DD
is "T/2=22.5.degree.". Note that, for the sake of simplicity, all
delay elements have the same rising delay amount and falling delay
amount.
[0145] (Starting of Driving of NMOS Transistor)
[0146] At time t1, in the level shifter LS0, a clock signal P0
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of an output signal Q0 starts
decreasing. In this case, a delayed output signal Q3' is at the
high level, and therefore, the PMOS transistor Mp1 is in the
non-drive state.
[0147] (Decrease in Voltage of Delayed Output Signal Q3')
[0148] At time t2, in the level shifter LS3, a clock signal P3
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q3 starts
decreasing. Also, the voltage value of a delayed output signal Q3'
starts decreasing, which is delayed by the rising delay amount (T)
in the delay element DD.
[0149] (Stopping of Driving of NMOS Transistor/Starting of Driving
of PMOS Transistor)
[0150] At time t3, in the level shifter LS0, the clock signal P0
falls, so that the NMOS transistor Mn1 goes into the non-drive
state. On the other hand, the delayed output signal Q3' goes to the
low level, so that the PMOS transistor Mp1 goes into the drive
state. Thereby, the voltage value of an output signal Q0 starts
increasing.
[0151] (Decrease in Voltage of Delayed Output Signal Q6')
[0152] At time t4, in the level shifter LS6, a clock signal P6
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of an output signal Q6 starts
decreasing. Also, the voltage value of a delayed output signal Q6'
starts decreasing, which is delayed by the falling delay amount (T)
in the delay element DD.
[0153] (Increase in Voltage of Delayed Output Signal Q3')
[0154] At time t5, in the level shifter LS3, the delayed output
signal Q6' goes to the low level, so that the PMOS transistor Mp1
goes into the drive state. Thereby, the voltage value of the output
signal Q3 starts increasing. Also, the voltage value of the delayed
output signal Q3' starts increasing, which is delayed by the rising
delay amount (T/2) in the delay element DD.
[0155] (Stopping of Driving of PMOS Transistor/Starting of Driving
of NMOS Transistor)
[0156] At time t6, in the level shifter LS0, the delayed output
signal Q3' goes to the high level, so that the PMOS transistor Mp1
goes into the non-drive state. On the other hand, the clock signal
P0 rises, so that the NMOS transistor Mn1 goes into the drive
state. Thereby, the voltage value of the output signal Q0 starts
decreasing.
[0157] Thus, in each of the level shifters LS0 to LS7, the NMOS
transistor Mn1 goes into the non-drive state before the PMOS
transistor Mp1 goes into the drive state, and the PMOS transistor
Mp1 goes into the non-drive state before the NMOS transistor Mn1
goes into the drive state. In other words, a drive period Ton(n) of
the NMOS transistor Mn1 and a drive period Ton(p) of the PMOS
transistor Mp1 do not overlap each other.
[0158] <Non-Overlapping Conditions>
[0159] Next, non-overlapping conditions in this embodiment will be
described with reference to FIG. 8. Here, level shifters
LS.sub.(k), LS.sub.(k+.alpha.), and LS.sub.(k+2.alpha.) will be
described as an example. Note that it is here assumed that the
rising delay amount and the falling delay amount in each delay
element are considered in terms of a "phase amount".
[0160] Firstly, symbols in the following expressions will be
described.
[0161] <<Delayed Output Signals>>
[0162] Q'.sub.(k+.alpha.): a delayed output signal of the level
shifter LS.sub.(k+.alpha.)
[0163] Q'.sub.(k+2.alpha.): a delayed output signal of the level
shifter LS.sub.(k+2.alpha.)
[0164] <<Signal Delay Amounts in Delay Element>>
[0165] D.sub.(DD.uparw.): a rising delay amount in the delay
element DD
[0166] D.sub.(DD.dwnarw.): a falling delay amount in the delay
element DD
[0167] Note that .uparw., .dwnarw., P.sub.(k), P.sub.(k+.alpha.),
P.sub.(k+2.alpha.), Q.sub.(k+.alpha.), Q.sub.(k+2.alpha.),
D.sub.(LS.uparw.), D.sub.(LS.dwnarw.), a phase relationship, and a
phase amount X are similar to those of FIG. 4.
[0168] (Drive Period of Transistor)
[0169] In order to satisfy the non-overlapping conditions, the
following [Expression 2-1] and [Expression 2-2] need to be
satisfied.
P.sub.(k).dwnarw..ltoreq.Q'.sub.(k+.alpha.).dwnarw. [Expression
2-1]
Q'.sub.(k+.alpha.).uparw..ltoreq.P.sub.(k).uparw.+360.degree.
[Expression 2-2]
[0170] Specifically, the falling edge of the delayed output signal
Q'(k+.alpha.) occurs subsequent in time to (or simultaneously with)
the falling edge P.sub.(k).dwnarw. of the clock signal P.sub.(k),
and the rising edge of the delayed output signal Q'.sub.(k+.alpha.)
occurs prior in time to (or simultaneously with) the rising edge
P.sub.(k).uparw. of the clock signal P.sub.(k).
[0171] (Timing of Occurrence of Edge of Delayed Output Signal)
[0172] In the case of FIG. 4, the falling delay amount and the
rising delay amount in each delay element DD are taken into
consideration, so that the falling edge Q'.sub.(k+.alpha.).dwnarw.
and the rising edge Q'.sub.(k+.alpha.).uparw. of the delayed output
signal Q'.sub.(k+.alpha.) are represented by [Expression 2-3] and
[Expression 2-4].
Q ` ( k + .alpha. ) .dwnarw. = Q ( k + .alpha. ) .dwnarw. + D ( DD
.dwnarw. ) = P ( k + .alpha. ) .uparw. + D ( LS .dwnarw. ) + D ( DD
.dwnarw. ) [ Expression 2 - 3 ] Q ` ( k + .alpha. ) .uparw. = W ( k
+ .alpha. ) .uparw. + D ( DD .uparw. ) = Q ` ( k + 2 .alpha. )
.dwnarw. + D ( LS .uparw. ) + D ( DD .uparw. ) = Q ( k + 2 .alpha.
) .dwnarw. + D ( DD .dwnarw. ) + D ( LS .uparw. ) + D ( DD .uparw.
) [ Expression 2 - 4 ] ##EQU00001##
[0173] As is similar to the case of FIG. 4, the falling edge
Q'.sub.(k+.alpha.).dwnarw. of the delayed output signal
Q'.sub.(k+.alpha.) depends on the timing of occurrence of the
rising edge P.sub.(k+.alpha.).uparw. of the clock signal
P.sub.(k+.alpha.), and the rising edge Q'.sub.(k+.alpha.).uparw. of
the delayed output signal Q'.sub.(k+.alpha.) depends on the timing
of occurrence of the rising edge P.sub.(k+2.alpha.).uparw. of the
clock signal P.sub.(k+2.alpha.).
[0174] (Phase Amount X)
[0175] (1) Initially, a lower limit value of the phase amount X is
obtained. Here, [Expression 2-3] is substituted into [Expression
2-1].
[0176] Also, since P.sub.(k).dwnarw.=P.sub.(k).uparw.+180.degree.
and P.sub.(k+2.alpha.).uparw.-P.sub.(k+.alpha.).uparw.=X,
[Expression
2-1]P.sub.(k).uparw.+180.degree..ltoreq.P.sub.(k+.alpha.).uparw.+D.sub.(L-
S.dwnarw.)+D.sub.(DD.dwnarw.)
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw..gtoreq.180.degree.-D.sub.(LS.d-
wnarw.)-D.sub.(DD.dwnarw.)
X.gtoreq.180.degree.-(D.sub.(LS.dwnarw.)+D.sub.(DD.dwnarw.))
[Expression 2-5]
[0177] Thus, [Expression 2-5] is obtained.
[0178] (2) Next, an upper limit value of the phase amount X is
obtained. Here, [Expression 2-4] is substituted into [Expression
2-2]. Also, it is assumed that
D.sub.(LS.dwnarw.)+D.sub.(DD.dwnarw.)+D.sub.(LS.uparw.)+D.sub.(DD.uparw.)-
=A. Note that, since
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw.=2X,
[Expression
2-2]P.sub.(k+2.alpha.).uparw.+A.ltoreq.P.sub.(k).uparw.+360.degree.
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw..ltoreq.360.degree.-A
2X.ltoreq.360.degree.-D.sub.(LS.dwnarw.)-D.sub.(LS.uparw.)-D.sub.(DD.dwn-
arw.)-D.sub.(DD.uparw.)
X.ltoreq.180.degree.-(1/2)(D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.)+D.sub.(D-
D.dwnarw.)+D.sub.(DD.uparw.)) [Expression 2-6]
[0179] Thus, [Expression 2-6] is obtained.
[0180] (3) Next, the range of the phase amount X is obtained.
[0181] Here, since D.sub.(LS.dwnarw.), D.sub.(DD.dwnarw.),
D.sub.(LS.uparw.), D.sub.(DD.uparw.)>0.degree. and
X>0.degree.,
[Expression 2-5]0.degree.<X
[Expression 2-6]X<180.degree.
Therefore,
0.degree.<X<180.degree. [Expression 2-7]
[0182] Thus, [Expression 2-7] is obtained.
[0183] (4) As described above, if the phase amount X satisfies
[Expression 2-5] and [Expression 2-6], the non-overlapping
conditions can be satisfied. Also, the possible range of the phase
amount X is represented by [Expression 2-7]. Specifically, although
the possible range of the phase amount X varies depending on the
falling delay amount and the rising delay amount in each level
shifter, the phase amount X which can satisfy the non-overlapping
conditions falls within the range of [Expression 2-7].
[0184] (Phase Delay Amounts D.sub.(DD.dwnarw.) and
D.sub.(DD.uparw.) in Delay Element)
[0185] Next, the falling delay amount D.sub.(LS.dwnarw.) and the
rising delay amount D.sub.(DD.uparw.) in the delay element DD are
obtained.
[Expression
2-5]D.sub.(DD.dwnarw.).gtoreq.180.degree.-D.sub.(LS.dwnarw.)-X
[Expression 2-8]
[Expression
2-6]D.sub.(DD.dwnarw.)+D.sub.(DD.uparw.).ltoreq.360.degree.-(D.sub.(LS.up-
arw.)+D.sub.(LS.uparw.))-2X [Expression 2-9]
[0186] By [Expression 2-8]-[Expression 2-9],
D.sub.(DD.uparw.).ltoreq.180.degree.-D.sub.(LS.uparw.)-X
[Expression 2-10]
[0187] As described above, if the signal delay amount of the delay
element DD is set so as to satisfy [Expression 2-8] and [Expression
2-10], the non-overlapping conditions can be satisfied without
changing the signal delay amount in the level shifter.
<Effect>
[0188] As described above, in each level shifter, the overlapping
of the current extraction period and the current supply period can
be eliminated, so that the occurrence of a through current can be
suppressed. Thereby, power consumption in each level shifter can be
reduced.
[0189] Also, since the current extraction period and the current
supply period do not substantially overlap, a delay amount in each
level shifter can be reduced. Thereby, the phase precision of the
output signal with respect to the clock signal can be improved.
[0190] Further, by adjusting a signal delay amount in the delay
element, the occurrence of a through current can be suppressed.
Therefore, the multiphase level shift system can be easily
constructed without changing the design of the level shifter.
[0191] Note that the falling delay amount is preferably larger than
the rising delay amount in the delay element. In this case, the
possible range of the phase amount X is broadened, so that the
multiphase level shift system can be easily constructed.
Third Embodiment
[0192] <Configuration>
[0193] FIG. 9 shows a configuration of a multiphase level shift
system according to a third embodiment of the present invention. In
this system, level shifters LS0 to LS7 each further include a PMOS
transistor Mp2 in addition to the NMOS transistor Mn1 and the PMOS
transistor Mp1 of FIG. 1. The PMOS transistor Mp2 and the PMOS
transistor Mp1 are connected in series between a power supply node
and an output node.
[0194] In each of the level shifters LS0 to LS7, the gate of the
PMOS transistor Mp2 receives an output signal from a level shifter
corresponding to a clock signal delayed by a phase amount Y
(X<Y<360.degree.-X) from the clock signal given to the NMOS
transistor Mn1. Also, the level shifters all have the same phase
amount Y. In FIG. 9, X=135.degree. and Y=180.degree..
[0195] <Phase Amount Y in Each Level Shifter>
[0196] FIG. 10 shows a phase relationship between a clock signal
given to the NMOS transistor Mn1 and an output signal given to the
PMOS transistor Mp2 in each of the level shifters LS0 to LS7 of
FIG. 9. Note that the phase relationship between the clock signal
given to the NMOS transistor Mn1 and the output signal given to the
PMOS transistor Mp1 in each of the level shifters LS0 to LS7 of
FIG. 9 is similar to that of FIG. 2, and therefore, the output
signal given to the PMOS transistor Mp1 is simplified by a dashed
line in FIG. 10.
[0197] In a level shifter LS.sub.(k) corresponding to a clock
signal P.sub.(k) having a k h phase, the NMOS transistor Mn1
receives the clock signal P.sub.(k), and the PMOS transistor Mp2
receives an output signal Q.sub.(k+.beta.) from a level shifter
LS.sub.(k+.beta.) corresponding to a clock signal P.sub.(k+.beta.).
The clock signal P.sub.(k+.beta.) is delayed by the phase amount Y
from the clock signal P.sub.(k). Here, ".beta." is an integer, and
.beta.=Y/T (T is a phase interval of clock signals). Note that,
when (k+.beta.)>(n-1), (k+.beta.) is a remainder which is left
when (k+.beta.) is divided by n. In FIG. 10, n=8 and
.beta.=180.degree./45.degree.=4.
[0198] <Operation>
[0199] Next, an operation of the multiphase level shift system of
FIG. 9 will be described with reference to FIG. 11. Note that, in
FIG. 11, both the falling delay amount and the rising delay amount
of a level shifter are assumed to be "22.5.degree.".
[0200] (Starting of Driving of NMOS Transistor)
[0201] At time t1, in the level shifter LS0, the clock signal P0
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q0 starts
decreasing. Also, in this case, since the output signal Q4 is at
the low level, the PMOS transistor Mp2 is in the drive state,
however, since the output signal Q3 is not at the low level, the
PMOS transistor Mp1 is in the non-drive state.
[0202] (Stopping of Driving of Both PMOS Transistors)
[0203] At time t2, in the level shifter LS0, the output signal Q4
goes to a level higher than the low level, so that the PMOS
transistor Mp2 goes into the non-drive state. Thereby, both the
PMOS transistors Mp1 and Mp2 go into the non-drive state.
[0204] (Decrease in Voltage of Output Signal Q3)
[0205] At time t3, in the level shifter LS3, the clock signal P3
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q3 in the level
shifter LS3 starts decreasing.
[0206] (Decrease in Voltage of Output Signal Q4/Stopping of Driving
of NMOS Transistor)
[0207] At time t4, in the level shifter LS4, the clock signal P4
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q4 starts
decreasing. On the other hand, at time t4, in the level shifter
LS0, the output signal Q3 is at the low level, and therefore, the
PMOS transistor Mp1 is in the drive state, however, since the
output signal Q4 is in a starting state of transition to the low
level, the PMOS transistor Mp2 is still in the non-drive state.
Also, at time t4, the clock signal P0 falls, so that the NMOS
transistor Mn1 is changed into the non-drive state.
[0208] (Starting of Driving Both PMOS Transistors)
[0209] At times t4 to t5, if the output signal Q4 goes to the low
level, the PMOS transistor Mp2 goes into the drive state in the
level shifter LS0. Therefore, both the PMOS transistors Mp1 and Mp2
go into the drive state, so that the voltage value of the output
signal Q0 starts increasing.
[0210] (Decrease in Voltage of Output Signal Q6)
[0211] At time t5, in the level shifter LS6, the clock signal P6
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q6 starts
decreasing.
[0212] (Decrease in Voltage of Output Signal Q7)
[0213] At time t6, in the level shifter LS7, the clock signal P7
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, the voltage value of the output signal Q7 starts
decreasing. On the other hand, at time t6, in the level shifter
LS3, the output signal Q6 is at the low level, and therefore, the
PMOS transistor Mp1 is in the drive state, however, since the
output signal Q7 is in a starting state of transition to the low
level, the PMOS transistor Mp2 is still in the non-drive state.
[0214] (Increase in Voltage of Output Signal Q3)
[0215] At times t6 to t7, if the output signal Q7 goes to the low
level, the PMOS transistor Mp2 goes into the drive state in the
level shifter LS3. Thereby, both the PMOS transistors Mp1 and Mp2
go into the drive state, so that the voltage value of the output
signal Q3 starts increasing.
[0216] (Stopping of Driving of PMOS Transistor/Starting of Driving
of NMOS Transistor)
[0217] At time t7, in the level shifter LS0, since the output
signal Q4 is at the low level, the PMOS transistor Mp2 is in the
drive state, however, since the output signal Q3 is at the high
level, the PMOS transistor Mp1 goes into the non-drive state. Also,
the clock signal P0 rises, so that the NMOS transistor Mn1 goes
into the drive state. Thereby, the voltage value of the output
signal Q0 starts decreasing.
[0218] Thus, in the level shifter LS0 as an example, during a
period in which the clock signal P0 is at the high level, there is
no period in which both the output signals Q3 and Q4 input to the
level shifter LS0 are at the low level. Also, in each of the level
shifters LS1 to LS7, a phase relationship between the clock signal
and the two output signals is similar to the phase relationship in
the level shifter LS0. Specifically, in each of the level shifters
LS0 to LS7, the NMOS transistor goes into the non-drive state
before both the PMOS transistors Mp1 and Mp2 go into the drive
state, and at least one of the PMOS transistors Mp1 and Mp2 goes
into the non-drive state before the NMOS transistor Mn1 goes into
the drive state. In other words, a drive period Ton(n) (current
extraction period) of the NMOS transistor Mn1 and a Ton(pp)
(current supply period) in which both the PMOS transistors Mp1 and
Mp2 are driven do not overlap each other.
[0219] Note that, at time t1 or the like, the timing of transition
of the drive state of the NMOS transistor and the timing of
transition of the drive state of the PMOS transistor may be the
same.
<Non-Overlapping Conditions>
[0220] Next, non-overlapping conditions in this embodiment will be
described with reference to FIG. 12. Here, level shifters
LS.sub.(k), LS.sub.(k+.alpha.), LS.sub.(k+.beta.), and
LS.sub.(k+.alpha.+.beta.) will be described as an example. Firstly,
symbols used in the following expressions will be described. Note
that .uparw., .dwnarw., P.sub.(k), P.sub.(k+.alpha.),
Q.sub.(k+.alpha.), Q.sub.(k+2.alpha.), D.sub.(LS.uparw.), and
D.sub.(LS.dwnarw.) are similar to those of FIG. 4.
[0221] <<Clock Signals>>
[0222] P.sub.(k+.beta.): a clock signal having a (k+.beta.).sup.th
phase
[0223] P.sub.(k+.alpha.+.beta.): clock signal having a
(k+.alpha.+.beta.).sup.th phase
[0224] <<Output Signals>>
[0225] Q.sub.(k+.beta.): an output signal of the level shifter
LS.sub.(k+.beta.)
[0226] Q.sub.(k+.alpha.+.beta.): an output signal of the level
shifter LS.sub.(k+.alpha.+.beta.)
[0227] <<Phase Relationships>>
P.sub.(k).uparw.<P.sub.(k+.alpha.).uparw.
P.sub.(k+.alpha.).uparw.<P.sub.(k+.beta.).uparw.<P.sub.(k+.alpha.+-
.beta.).uparw.
P.sub.(k+.alpha.+.beta.).uparw.<(P.sub.(k).uparw.+360.degree.)
P.sub.(k).dwnarw.=P.sub.(k).uparw.+180.degree.
Q.sub.(k+.alpha.).dwnarw.<Q.sub.(k+.beta.).dwnarw.
Q.sub.(k+.alpha.).uparw.<Q.sub.(k+.beta.).uparw.
[0228] <<Phase Amount X, Phase Amount Y>>
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.=P.sub.(k+.alpha.+.beta.).uparw-
.-P.sub.(k+.beta.).uparw.=X
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.>0.degree.X>0.degree.
P.sub.(k+.beta.).uparw.-P.sub.(k).uparw.=Y
P.sub.(k+.beta.).uparw.-P.sub.(k).uparw.>0.degree.Y>0.degree.
P.sub.(k+.beta.).uparw.-P.sub.(k).uparw.>P.sub.(k+.alpha.).uparw.-P.s-
ub.(k).uparw.Y>X
[0229] A phase amount X which is a phase delay amount of the clock
signal P.sub.(k+.alpha.) with respect to the clock signal P.sub.(k)
is defined by the above-described expression. Also, a phase delay
amount of the clock signal P.sub.(k+.alpha.+.beta.) with respect to
the clock signal P.sub.(k+.beta.) is equal to a phase delay amount
of the clock signal P.sub.(k+.alpha.) with respect to the clock
signal P.sub.(k). Also, a phase amount Y which is a phase delay
amount of the clock signal P.sub.(k+.beta.) with respect to the
clock signal P.sub.(k) is defined by the above-described
expression. Further, a relationship in magnitude between the phase
amount X and the phase amount Y is represented by the
above-described expression.
[0230] (Drive Period of Transistor)
[0231] In the level shifter LS.sub.(k), during a period from the
rising edge P.sub.(k).uparw. to the falling edge P.sub.(k).dwnarw.
of the clock signal P.sub.(k), the NMOS transistor Mn1 is in the
drive state, so that a current is extracted from the output node to
the ground node.
[0232] Also, during a period from the falling edge
Q.sub.(k+.alpha.).dwnarw. to the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.),
the PMOS transistor Mp1 is in the drive state. On the other hand,
during a period from the falling edge Q.sub.(k+.beta.).dwnarw. to
the rising edge Q.sub.(k+.beta.).uparw. of the output signal
Q.sub.(k+.beta.), the PMOS transistor Mp2 is in the drive state.
Since Q.sub.(k+.alpha.).uparw.<Q.sub.(k+.beta.).uparw., during a
period from the falling edge Q.sub.(k+.beta.).dwnarw. of the output
signal Q.sub.(k+.beta.) to the rising edge Q.sub.(k+.alpha.).uparw.
of the output signal Q.sub.(k+.alpha.), both the output signals
Q.sub.(k+.alpha.) and Q.sub.(k+.beta.) are at the low level, so
that both the PMOS transistors Mp1 and Mp2 are in the drive state,
and therefore, a current is supplied from the power supply node to
the output node.
[0233] Therefore, in order to satisfy the non-overlapping
conditions, the following [Expression 3-1] and [Expression 3-2]
need to be satisfied.
P.sub.(k).dwnarw..ltoreq.Q.sub.(k+.beta.).dwnarw. [Expression
3-1]
Q.sub.(k+.alpha.).uparw..ltoreq.P.sub.(k).uparw.+360.degree.
[Expression 3-2]
[0234] Specifically, the falling edge Q.sub.(k+.beta.).dwnarw. of
the output signal Q.sub.(k+.beta.) occurs subsequent in time to (or
simultaneously with) the falling edge P.sub.(k).dwnarw. of the
clock signal P.sub.(k), and the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.)
occurs prior in time to (or simultaneously with) the rising edge
P.sub.(k).uparw. of the clock signal P.sub.(k).
[0235] (Timing of Occurrence of Edge of Output Signal)
[0236] In the level shifter LS.sub.(k+.beta.), if the rising edge
P.sub.(k+.beta.).uparw. of the clock signal P.sub.(k+.beta.)
occurs, the voltage value of the output signal Q.sub.(k+.beta.)
starts decreasing. On the other hand, in the level shifter
LS.sub.(k+.alpha.), if the falling edge
Q.sub.(k+.alpha.+.beta.).dwnarw. of the output signal
Q.sub.(k+.alpha.+.beta.) occurs after the occurrence of the falling
edge Q.sub.(k+2.alpha.).dwnarw. of the output signal
Q.sub.(k+2.alpha.), the voltage value of the output signal
Q.sub.(k+.alpha.) starts increasing. Further, in the level shifter
LS.sub.(k+.alpha.+.beta.), if the rising edge
P.sub.(k+.alpha.+.beta.).uparw. of the clock signal
P.sub.(k+.alpha.+.beta.) occurs, the voltage value of the output
signal Q.sub.(k+.alpha.+.beta.) starts decreasing.
[0237] Here, taking into consideration a rising delay amount and a
falling delay amount in each level shifter, the falling edge
Q.sub.(k+.beta.).dwnarw. of the output signal Q.sub.(k+.beta.) and
the rising edge Q.sub.(k+.alpha.).uparw. of the output signal
Q.sub.(k+.alpha.) are represented by [Expression 3-3] and
[Expression 3-4].
Q ( k + .beta. ) .dwnarw. = P ( k + .beta. ) .uparw. + D ( LS
.dwnarw. ) [ Expression 3 - 3 ] Q ( k + .alpha. ) .uparw. = Q ( k +
.alpha. + .beta. ) .dwnarw. + D ( LS .uparw. ) = P ( k + .alpha. +
.beta. ) .uparw. + D ( LS .dwnarw. ) + D ( LS .uparw. ) [
Expression 3 - 4 ] ##EQU00002##
[0238] Specifically, the falling edge Q.sub.(k+.beta.).dwnarw. of
the output signal Q.sub.(k+.beta.) depends on the timing of
occurrence of the rising edge P.sub.(k+.beta.).uparw. of the clock
signal P(k+.beta.), and the rising edge Q.sub.(k+.alpha.).uparw. of
the output signal Q.sub.(k+.alpha.) depends on the rising edge
P.sub.(k+.alpha.+.alpha.).uparw. of the clock signal
P.sub.(k+.alpha.+.beta.).
[0239] (Phase Amount X, Phase Amount Y)
[0240] (1) Initially, [Expression 3-3] is substituted into
[Expression 3-1].
[0241] Also, since P.sub.(k).dwnarw.=P.sub.(k)+180.degree. and
P.sub.(k+.beta.).uparw.-P.sub.(k).uparw.=Y,
[Expression
3-1]P.sub.(k).uparw.+180.degree..ltoreq.P.sub.(k+.beta.).uparw.+D.sub.(LS-
.dwnarw.)
P.sub.(k+.beta.).uparw.-P.sub.(k).uparw..gtoreq.180.degree.-D.sub.(LS.dw-
narw.)
Y.gtoreq.180.degree.-D.sub.(LS.dwnarw.) [Expression 3-5]
[0242] Thus, [Expression 3-5] is obtained.
[0243] (2) Next, [Expression 3-4] is substituted into [Expression
3-2].
[0244] Also, since
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.=P.sub.(k+.alpha.+.beta.).uparw.-
-P.sub.(k+.beta.).uparw.=X, and
P.sub.(k+.beta.).uparw.-P.sub.(k).uparw.=Y,
[0245] [Expression 3-7]
P.sub.(k+.alpha.+.beta.).uparw.+D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.).lto-
req.P.sub.(k).uparw.+360.degree.
P.sub.(k+.alpha.+.beta.).uparw.-P.sub.(k).uparw..ltoreq.360.degree.-D.su-
b.(LS.dwnarw.)-D.sub.(LS.uparw.)
X+Y.ltoreq.360.degree.-D.sub.(LS.dwnarw.)-D.sub.(LS.uparw.)
[Expression 3-6]
[0246] Thus, [Expression 3-6] is obtained.
[0247] (3) Next, the phase amount X is obtained. Here, [Expression
3-5]-[Expression 3-6] is calculated. Also, since
X>0.degree.,
[Expression 3-5]-[Expression
3-6]X.ltoreq.180.degree.-D.sub.(LS.uparw.)
0.degree.<X.ltoreq.180.degree.-D.sub.(LS.uparw.) [Expression
3-7]
[0248] Also, since D.sub.(LS.uparw.)>0.degree.,
[Expression 3-7]0.degree.<X<180.degree. [Expression 3-8]
[0249] Thus, [Expression 3-7] and [Expression 3-8] are
obtained.
[0250] (4) Next, the phase amount Y is obtained. Here, according to
[Expression 3-5] and [Expression 3-6],
180.degree.-D.sub.(LS.dwnarw.).ltoreq.Y.ltoreq.360.degree.-D.sub.(LS.dwn-
arw.)-D.sub.(LS.uparw.)-X [Expression 3-9]
[0251] Also, D.sub.(LS.dwnarw.)>0.degree.,
D.sub.(LS.uparw.)>0.degree., and Y>X,
[Expression 3-9]X<Y<360.degree.-X [Expression 3-10]
[0252] Thus, [Expression 3-9] and [Expression 3-10] are
obtained.
[0253] (5) As described above, if the phase amount X satisfies
[Expression 3-7] and the phase amount Y satisfies [Expression 3-9],
the non-overlapping conditions can be satisfied. Also, the possible
range of the phase amount X is represented by [Expression 3-8], and
the possible range of the phase amount Y is represented by
[Expression 3-10]. Specifically, although the possible range of the
phase amount X and the possible range of the phase amount Y vary
depending on the falling delay amount and the rising delay amount
in a level shifter, the phase amount X and the phase amount Y which
can satisfy the non-overlapping conditions fall within the ranges
represented by [Expression 3-8] and [Expression 3-10],
respectively.
<Effect>
[0254] As described above, in each level shifter, the overlapping
of the current extraction period and the current supply period can
be eliminated, so that the occurrence of a through current can be
suppressed. Thereby, power consumption in each level shifter can be
reduced.
[0255] Also, since the current supply period and the current
extraction period do not substantially overlap, the delay amount in
each level shifter can be reduced. Thereby, the phase precision of
the output signal with respect to the clock signal can be
improved.
[0256] Further, according to FIG. 12 and [Expression 3-4], the
rising edge Q.sub.(k+.alpha.).uparw. of the output signal
Q.sub.(k+.alpha.) depends on the timing of occurrence of the rising
edge of the clock signal P.sub.(k+.alpha.+.beta.).uparw. whose
phase delay amount is the phase amount Y. In other words, by
adjusting the phase amount Y, the timing of occurrence of the
rising edge of the output signal can be adjusted. Thereby, the duty
ratio of the output signal can also be adjusted.
[0257] Note that, in each level shifter, the output signals given
to the PMOS transistors Mp1 and Mp2 may be switched with the other
transistor. For example, in the level shifter LS0, the output
signal Q4 may be given to the gate of the PMOS transistor Mp1, and
the output signal Q3 may be given to the gate of the PMOS
transistor Mp2.
Fourth Embodiment
[0258] <Multiphase Level Shift System>
[0259] FIG. 13 shows a configuration of a multiphase level shift
system according to a fourth embodiment of the present invention.
In this system, level shifters LS0 to LS7 each include an NMOS
transistor Mn2 in addition to the NMOS transistor Mn1 and the PMOS
transistor Mp1 of FIG. 1. The NMOS transistor Mn2 and the NMOS
transistor Mn1 are connected in series between a ground node and an
output node.
[0260] In each of the level shifters LS0 to LS7, the gate of the
NMOS transistor Mn2 receives a clock signal advanced by a phase
amount Z (0.degree.<Z<180.degree.) from the clock signal
given to the gate of the NMOS transistor Mn1. Also, the level
shifters all have the same phase amount Z. In FIG. 13,
X=135.degree. and Z=45.degree..
[0261] <Phase Amount Y in Each Level Shifter>
[0262] FIG. 14 shows a phase relationship between a clock signal
given to the NMOS transistor Mn1, a clock signal given to the NMOS
transistor Mn2, and an output signal given to the PMOS transistor
Mp1 in each of the level shifters LS0 to LS7 of FIG. 13.
[0263] In a level shifter LS.sub.(k) corresponding to a clock
signal P.sub.(k) having a k.sup.th phase, the NMOS transistor Mn1
receives the clock signal P.sub.(k), the NMOS transistor Mn2
receives a clock signal P.sub.(k-.gamma.), and the PMOS transistor
Mp1 receives an output signal Q.sub.(k+.alpha.) from a level
shifter LS.sub.(k+.alpha.) corresponding to a clock signal
P.sub.(k+.alpha.). The clock signal P.sub.(k-.gamma.) is advanced
by the phase amount Z from the clock signal P.sub.(k). Here,
".gamma." is an integer and .gamma.=Z/T (T is a phase interval of
clock signals). Note that, when (k-.gamma.)<0, (k-.gamma.) is a
remainder which is left when dividing (k+.gamma.+n) by n. In FIG.
14, n=8, .alpha.=135.degree./45.degree.=3, and
.gamma.=45.degree./45.degree.=1.
<Operation>
[0264] Next, an operation of the multiphase level shift system of
FIG. 13 will be described with reference to FIG. 15. Note that, in
FIG. 15, both a falling delay amount and a rising delay amount in a
level shifter are assumed to be "22.5.degree.".
[0265] (Starting of Driving of Both NMOS Transistors)
[0266] At time t1, in the level shifter LS0, the clock signal P0
rises, so that the NMOS transistor Mn1 goes into the drive state.
In this case, since the clock signal P7 is at the high level, the
NMOS transistor Mn2 is also in the drive state. Thereby, the
voltage value of the output signal Q0 starts decreasing.
[0267] (Decrease in Voltage of Output Signal Q3/Stopping of Driving
of NMOS Transistor)
[0268] At time t2, in the level shifter LS3, the clock signal P2
rises, so that the NMOS transistor Mn2 goes into the drive state.
Next, at time t3, in the level shifter LS3, the clock signal P3
rises, so that the NMOS transistor Mn1 goes into the drive state.
Therefore, both the NMOS transistors Mn1 and Mn2 go into the drive
state, so that the voltage value of the output signal Q3 starts
decreasing. On the other hand, in the level shifter LS0, the clock
signal P7 falls, so that the NMOS transistor Mn2 goes into the
non-drive state.
[0269] (Starting of Driving of PMOS Transistor)
[0270] At times t3 to t4, if the output signal Q3 goes to the low
level, the PMOS transistor Mp1 goes into the drive state in the
level shifter LS0. Thereby, the voltage value of the output signal
Q0 starts increasing.
[0271] (Stopping of Driving of Both NMOS Transistors)
[0272] At time t4, in the level shifter LS0, the clock signal P0
falls, so that the NMOS transistor Mn1 goes into the non-drive
state. Thereby, both the NMOS transistors Mn1 and Mn2 go into the
non-drive state.
[0273] (Decrease in Voltage of Output Signal Q6)
[0274] At time t5, in the level shifter LS6, the clock signal P5
rises, so that the NMOS transistor Mn2 goes into the drive state.
At time t6, in the level shifter LS6, the clock signal P6 rises, so
that the NMOS transistor Mn1 goes into the drive state. Thereby,
both the NMOS transistors Mn1 and Mn2 go into the drive state, so
that the voltage value of the output signal Q6 starts
decreasing.
[0275] (Increase in Voltage of Output Signal Q3)
[0276] At times t6 to t7, if the output signal Q6 goes to the low
level, the PMOS transistor Mp1 goes into the drive state in the
level shifter LS3. Thereby, the voltage value of the output signal
Q3 starts increasing.
[0277] (Stopping of Driving of PMOS Transistor)
[0278] At time t7, in the level shifter LS0, the output signal Q3
goes to the high level, so that the PMOS transistor Mp1 goes into
the non-drive state. On the other hand, the clock signal P7 rises,
so that the NMOS transistor Mn2 goes into the drive state.
[0279] (Starting of Driving of Both NMOS Transistors)
[0280] At time t8, in the level shifter LS0, the clock signal P0
rises, so that the NMOS transistor Mn1 goes into the drive state.
Thereby, both the NMOS transistors Mn1 and Mn2 go into the drive
state, so that the voltage value of the output signal Q0 starts
decreasing.
[0281] Thus, in the level shifter LS0 as an example, during a
period in which both the clock signals P0 and P7 are at the high
level, there is no period in which the output signal Q3 input to
the level shifter LS0 is at the low level. Also, in each of the
level shifters LS1 to LS7, a phase relationship between the two
clock signals and the output signal is similar to the phase
relationship in the level shifter LS0. Specifically, in each of the
level shifters LS0 to LS7, at least one of the NMOS transistors Mn1
and Mn2 goes into the non-drive state before the PMOS transistor
Mp1 goes into the drive state, and the PMOS transistor Mp1 goes
into the non-drive state before both the NMOS transistors Mn1 and
Mn2 go into the drive state. In other words, a period Ton(nn)
(current extraction period) in which both the NMOS transistors Mn1
and Mn2 are driven and a drive period Ton(p) (current supply
period) of the PMOS transistor Mp1 do not overlap each other.
[0282] Note that, at time t1 or the like, the timing of transition
of the drive state of the NMOS transistor and the timing of
transition of the drive state of the PMOS transistor may
simultaneously occur.
[0283] <Non-Overlapping Conditions>
[0284] Next, non-overlapping conditions in this embodiment will be
described with reference to FIG. 16. Here, the level shifters
LS.sub.(k), LS.sub.(k+.alpha.), and LS.sub.(k+2.alpha.) will be
described as an example. Firstly, symbols used in the following
expressions will be described. Note that P.sub.(k),
P.sub.(k+.alpha.), P.sub.(k+2.alpha.), Q.sub.(k+.alpha.),
Q.sub.(k+2.alpha.), .uparw., .dwnarw., D.sub.(LS.uparw.), and
D.sub.(LS.dwnarw.) are similar to those of FIG. 4.
[0285] <<Clock Signals>>
[0286] P.sub.(k-.gamma.): a clock signal having a
(k-.gamma.).sup.th phase
[0287] <<Phase Relationships>>
P.sub.(k-.gamma.).uparw.<P.sub.(k).uparw.<P.sub.(k-.gamma.).dwnarw-
.<P.sub.(k).dwnarw.<(P.sub.(k).uparw.+360.degree.)
P.sub.(k-.gamma.).dwnarw.=P.sub.(k-.gamma.).uparw.+180.degree.
[0288] <<Phase Amount X, Phase Amount Z>>
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.=P.sub.(k+2.alpha.).uparw.-P.su-
b.(k+.alpha.).uparw.=X
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw.=2X
P.sub.(k+2.alpha.).uparw.-P.sub.(k+.alpha.).uparw.>0.degree.X>0.de-
gree.
P.sub.(k).uparw.-P.sub.(k-.gamma.).uparw.=Z
P.sub.(k).uparw.<P.sub.(k-.gamma.)P.sub.(k).uparw.<P.sub.(k-.gamma-
.).uparw.+180.degree.Z<180.degree.
P.sub.(k).uparw.-P.sub.(k-.gamma.).uparw.>0.degree.Z>0.degree.
[0289] The phase amount Z which is a phase advance amount of the
clock signal P.sub.(k-.gamma.) with respect to the clock signal
P.sub.(k) is defined by the above-described expression.
[0290] (Drive Period of Transistor)
[0291] In the level shifter LS.sub.(k), during a period from the
rising edge P.sub.(k).uparw. to the falling edge P.sub.(k).dwnarw.
of the clock signal P.sub.(k), the NMOS transistor Mn1 is in the
drive state. On the other hand, during a period from the rising
edge P.sub.(k-.gamma.).uparw. to the falling edge
P.sub.(k-.gamma.).dwnarw. of the clock signal P.sub.(k-.gamma.),
the NMOS transistor Mn2 is in the drive state.
[0292] Since P.sub.(k-.gamma.).uparw.<P.sub.(k).uparw., during a
period from the rising edge P.sub.(k).uparw. of the clock signal
P.sub.(k) to the falling edge P.sub.(k-.gamma.).dwnarw. of the
clock signal P.sub.(k-.gamma.), both the clock signals P.sub.(k)
and P.sub.(k-.gamma.) are at the high level (e.g., higher than or
equal to the threshold voltage of the NMOS transistor), and
therefore, both the NMOS transistors Mn1 and Mn2 are in the drive
state, so that a current is extracted from the output node to the
ground node.
[0293] Therefore, in order to satisfy the non-overlapping
conditions, the following [Expression 4-1] and [Expression 4-2]
need to be satisfied.
P.sub.(k-.gamma.).dwnarw..ltoreq.Q.sub.(k+.alpha.).dwnarw.
[Expression 4-1]
Q.sub.(k+.alpha.).uparw..ltoreq.P.sub.(k).uparw.+360.degree.
[Expression 4-2]
[0294] Specifically, the falling edge Q.sub.(k+.alpha.), of the
output signal Q.sub.(k+.alpha.) occurs subsequent in time to (or
simultaneously with) the falling edge P.sub.(k-.gamma.) of the
clock signal P.sub.(k-.gamma.), and the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.)
occurs prior in time to (or simultaneously with) the rising edge
P.sub.(k) t of the clock signal P.sub.(k).
[0295] (Timing of Occurrence of Edge of Output Signal)
[0296] In the level shifter LS.sub.(k+.alpha.), when the rising
edge P.sub.(k+.alpha.).uparw. of the clock signal P.sub.(k+.alpha.)
occurs, the voltage value of the output signal Q.sub.(k+.alpha.)
starts decreasing. Also, when the falling edge
Q.sub.(k+2.alpha.).dwnarw. of the output signal occurs, the voltage
value of the output signal Q.sub.(k+.alpha.) starts increasing.
Further, in the level shifter LS.sub.(k+2.alpha.), when the rising
edge P.sub.(k+2.alpha.).uparw. of the clock signal
P.sub.(k+2.alpha.) occurs, the voltage value of the output signal
Q.sub.(k+2.alpha.) starts decreasing.
[0297] Here, taking into consideration a rising delay amount and a
falling delay amount in each level shifter, the falling edge
Q.sub.(k+.alpha.).dwnarw. and the rising edge
Q.sub.(k+.alpha.).uparw. of the output signal Q.sub.(k+.alpha.) are
represented by [Expression 4-3] and [Expression 4-4].
Q ( k + .alpha. ) .dwnarw. = P ( k + .alpha. ) .uparw. + D ( LS
.dwnarw. ) [ Expression 4 - 3 ] Q ( k + .alpha. ) .uparw. = Q ( k +
2 .alpha. ) .dwnarw. + D ( LS .uparw. ) = P ( k + 2 .alpha. )
.uparw. + D ( LS .dwnarw. ) + D ( LS .uparw. ) [ Expression 4 - 4 ]
##EQU00003##
[0298] Specifically, the falling edge Q.sub.(k+.alpha.).dwnarw. of
the output signal Q.sub.(k+.alpha.) depends on the timing of
occurrence of the rising edge P.sub.(k+.alpha.).uparw. of the clock
signal P.sub.(k+.alpha.), and the rising edge of the output signal
Q.sub.(k+.alpha.).uparw. depends on the timing of occurrence of the
rising edge P.sub.(k+2.alpha.).uparw. of the clock signal
P.sub.(k+2.alpha.).
[0299] (Phase Amount X, Phase Amount Z)
[0300] (1) Initially, [Expression 4-3] is substituted into
[Expression 4-1].
[0301] Also, since
P.sub.(k-.gamma.).dwnarw.=P.sub.(k-.gamma.).uparw.+180.degree.,
P.sub.(k+.alpha.).uparw.-P.sub.(k).uparw.=X, and
P.sub.(k).uparw.-P.sub.(k-.gamma.).uparw.=Z.
[Expression
4-1]P.sub.(k-.gamma.).uparw.+180.degree..ltoreq.P.sub.(k+.alpha.).uparw.+-
D.sub.(LS.dwnarw.)
P.sub.(k+.alpha.).uparw.-P.sub.(k-.gamma.).uparw..gtoreq.180.degree.-D.s-
ub.(LS.dwnarw.)
X+Z.gtoreq.180.degree.-D.sub.(LS.dwnarw.) [Expression 4-5]
[0302] Thus, [Expression 4-5] is obtained.
[0303] (2) Next, [Expression 4-4] is substituted into [Expression
4-2].
[0304] Also, since
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw.=2X,
[Expression
4-2]P.sub.(k+2.alpha.).uparw.+D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.).ltoreq-
.P.sub.(k).uparw.+360.degree.
P.sub.(k+2.alpha.).uparw.-P.sub.(k).uparw..ltoreq.360.degree.-D.sub.(LS.-
dwnarw.)-D.sub.(LS.uparw.)
2X.ltoreq.360.degree.-D.sub.(LS.dwnarw.)-D.sub.(LS.uparw.)
X.ltoreq.180.degree.-(1/2)(D.sub.(LS.dwnarw.)+D.sub.(LS.uparw.))
[Expression 4-6]
[0305] Thus, [Expression 4-6] is obtained.
[0306] (3) Next, the phase amount X is obtained. Here, since
[Expression 4-6] and X>0.degree.,
0.degree.<X.ltoreq.180.degree.-(1/2)(D.sub.(LS.dwnarw.)+D.sub.(LS.upa-
rw.)) [Expression 4-7]
[0307] Also, since D.sub.(LS.dwnarw.),
D.sub.(LS.uparw.)>0.degree.,
[Expression 4-7]0.degree.<X<180.degree. [Expression 4-8]
[0308] Thus, [Expression 4-8] and [Expression 4-7] are
obtained.
[0309] (4) Next, the phase amount Z is obtained. Here, since
[Expression 4-5] and Z<180.degree.,
180.degree.-D.sub.(LS.dwnarw.)-X.ltoreq.Z<180.degree.
[Expression 4-9]
[0310] Also, since D.sub.(LS.dwnarw.)>0.degree., X>0.degree.,
and Z>0.degree.,
[Expression 4-9]180.degree.-X<Z<180.degree.
0.degree.<Z<180.degree. [Expression 4-10]
[0311] Thus, [Expression 4-9] and [Expression 4-10] are
obtained.
[0312] (5) As described above, if the phase amount X satisfies
[Expression 4-7] and the phase amount Z satisfies [Expression 4-9],
the non-overlapping conditions can be satisfied. Also, the possible
range of the phase amount X is represented by [Expression 4-8], and
the possible range of the phase amount Z is as represented by
[Expression 4-10]. Specifically, the possible range of the phase
amount X and the possible range of the phase amount Z vary
depending on the falling delay amount and the rising delay amount
of a level shifter, the phase amount X which can satisfy the
non-overlapping conditions falls within the range represented by
[Expression 4-8], and the phase amount Z falls within the range
represented by [Expression 4-10].
<Effect>
[0313] As described above, in each level shifter, the overlapping
of the current extraction period and the current supply period can
be eliminated, so that the occurrence of a through current can be
suppressed. Thereby, power consumption in each level shifter can be
reduced.
[0314] Also, since the current extraction period and the current
supply period do not overlap, a delay amount in each level shifter
can be reduced. Thereby, the phase precision of the output signal
with respect to the clock signal can be improved.
[0315] Also, in general, the amplitude of the clock signal is
smaller than the amplitude of the output signal, and therefore,
power required for charging and discharging an NMOS transistor
(charging and discharging power) is smaller than charging and
discharging power for a PMOS transistor. In other words, charging
and discharging power for the level shifter of FIG. 13 is smaller
than charging and discharging power for the level shifter of FIG.
9. Therefore, in this embodiment, power consumption can be further
reduced than in the multiphase level shift system of FIG. 9.
[0316] Note that, in each level shifter, the clock signals given to
the NMOS transistors Mn1 and Mn2 may be switched with the other
transistor. For example, in the level shifter LS0, the clock signal
P7 may be given to the gate of the NMOS transistor Mn1, and the
clock signal P0 may be given to the gate of the NMOS transistor
Mn2.
Fifth Embodiment
[0317] <Configuration>
[0318] FIG. 17 shows a configuration of a multiphase level shift
system according to a fifth embodiment of the present invention. In
this system, level shifters LS0 to LS7 further include a resistance
element RR in addition to the NMOS transistor Mn1 and the PMOS
transistor Mp1 of FIG. 1.
[0319] In each of the level shifters LS0 to LS7, the resistance
element RR is connected between an output node (a connection point
of the transistors Mn1 and Mp1) of the level shifter, and an output
node of a level shifter corresponding to a clock signal whose phase
delay amount with respect to a clock signal given to the gate of
the NMOS transistor Mn1 of the level shifter is a phase amount T
(phase interval). In FIG. 17, T=45.degree. and X=135.degree..
[0320] In other words, in the multiphase level shift system of FIG.
17, the output nodes of the level shifters LS0 to LS7 are connected
via a resistor network.
<Resistor Network>
[0321] FIG. 18 shows a phase relationship between a clock signal
given to the NMOS transistor Mn1, an output signal given to the
PMOS transistor Mp1, and an output signal connected via the
resistance element RR to the output node, in each of the level
shifters LS0 to LS7 of FIG. 17.
[0322] In a level shifter LS.sub.(k) corresponding to a clock
signal P.sub.(k) having the k.sup.th phase, one end of the
resistance element RR is connected to the output node of the level
shifter LS.sub.(k), and the other end of the resistance element RR
is connected to the output node of a level shifter LS.sub.(k+1).
The level shifter LS.sub.(k+1) receives a clock signal P.sub.(k+1)
whose phase is delayed by the phase amount T from the clock signal
P.sub.(k) given to the level shifter LS.sub.(k). Here, when
(k+1)>(n-1), (k+1) is a remainder which is left when (k+1) is
divided by n. In FIG. 18, n=8, T=45.degree., and
.alpha.=135.degree./45.degree.=3.
<Operation>
[0323] Next, an operation of the multiphase level shift system of
FIG. 17 will be described. Note that a basic operation is similar
to that of the multiphase level shift system of FIG. 1, and
therefore, will be described with reference to FIG. 3.
[0324] For example, at time t4, output signals Q0, Q1, and Q2 are
all in a transition process from the low level to the high level.
Here, in the level shifter LS1, if device noise, a device variation
or the like occurs, the voltage value or through rate of the output
signal Q1 is changed, so that the phase of the output signal Q1 is
likely to be deviated from the center between the phase of the
output signal Q0 and the phase of the output signal Q2. In the
multiphase level shift system of FIG. 17, the output node of the
level shifter LS0 is connected via the resistance element RR to the
output node of the level shifter LS1, and the output node of the
level shifter LS1 is connected via the resistance element RR to the
output node of the level shifter LS2, so that a variation in
voltage at the output node of the level shifter LS1 (i.e., a
variation in voltage of the output signal Q1) is suppressed.
[0325] Thus, even if noise or a variation occurs in the level
shifter LS.sub.(k), the phase of the output signal Q.sub.(k) of the
level shifter LS.sub.(k) can be interpolated using adjacent phases,
so that a deterioration in phase precision can be suppressed.
<Effect>
[0326] As described above, a phase variation of the output signal
in each level shifter is interpolated using adjacent phases, so
that the phase precision of the output signal can be further
improved.
[0327] Note that the resistor network of this embodiment is
applicable not only to the first embodiment, but also to the
second, third, and fourth embodiments.
[0328] Further, as shown in FIG. 19, the resistor network is also
applicable to another multiphase level shift system. The multiphase
level shift system of FIG. 19 comprises level shifters LS50 to LS57
corresponding to clock signals P0 to P7, and resistance elements
RR0 to RR7 corresponding to the level shifters LS50 to LS57. The
level shifters LS50 to LS57 each perform voltage conversion with
respect to the corresponding clock signal and output an output
signal having a phase corresponding to the clock signal from the
output node. In other words, the phase interval of output signals
Q0 to Q7 is equal to the phase interval (phase amount
T=360.degree./n) of the clock signals P0 to P7. Also, the level
shifters LS50 to LS57 may each have, for example, a configuration
as shown in FIG. 22 or FIG. 24, or other configurations. The
resistance elements RR0 to RR7 are each connected between the
output node of the corresponding level shifter, and the output node
of a level shifter having an adjacent phase with respect to that
corresponding level shifter (a level shifter corresponding to a
clock signal whose phase delay amount with respect to a clock
signal corresponding to that corresponding level shifter is the
phase amount T (phase interval)). Note that, in FIG. 19, n=8,
T=45.degree.. With such a configuration, a phase variation of the
output signal of each level shifter is interpolated using adjacent
phases, so that the phase precision of the output signal can be
further improved.
Other Embodiments
[0329] Although eight clock signals (i.e., clock signals having
eight phases) are assumed in each of the above-described
embodiments, the present invention is also applicable to clock
signals having an even number of phases other than eight phases.
Also, the larger the number of phases of clock signals, the larger
the number of clock signals which can be selected as clock signals
P.sub.(k+.alpha.), P.sub.(k+.beta.), and P.sub.(k-.gamma.). For
example, in [Expression 1-5], [Expression 1-6], and [Expression
1-8], since X=T.alpha. (.alpha. is an integer),
[Expression 1-5](1/T)(180-D.sub.(LS.dwnarw.)).ltoreq..alpha.
[Expression
1-6].alpha..ltoreq.(1/T)(180.degree.-(1/2)(D.sub.(LS.dwnarw.)+D.sub.(LS.u-
parw.)))
[Expression 1-8]0.degree.<.alpha.<180.degree./T
[0330] Specifically, the larger the number of phases of clock
signals, the smaller the phase interval (phase amount T) of the
clock signals, i.e., the larger the number of clock signals which
can be selected as the clock signal P.sub.(k+.alpha.), so that the
multiphase level shift system can be easily constructed.
[0331] Also, the multiphase level shift system of each embodiment
is applicable not only to an even number of clock signals (i.e.,
clock signals having an even number of phases), but also to an odd
number of clock signals (i.e., clock signals having an odd number
of phases). When a multiphase level shift system is applied to
clock signals having an odd number of phases, one level shifter
including four transistors is required per clock signal in
conventional configurations whereas, in the multiphase level shift
system of each embodiment, each level shifter includes two or three
transistors, so that the circuit scale can be further reduced than
in conventional configurations.
[0332] Also, regarding the phases of a rising edge and a falling
edge of the output signal, for example, timing with which the
output signal reaches the threshold voltage .DELTA.Vt (or the low
level) (i.e., timing with which the PMOS transistor goes from the
non-drive state into the drive state) may be the phase of the
rising edge of the output signal, and timing with which the output
signal reaches the threshold voltage .DELTA.Vt (or the low level)
(i.e., the PMOS transistor goes from the drive state into the
non-drive state) may be the phase of the falling edge of the output
signal.
INDUSTRIAL APPLICABILITY
[0333] As described above, the multiphase level shift system of the
present invention can suppress the occurrence of a through current
in a level shifter, and therefore, is useful as, for example, a
system for performing voltage conversion with respect to clock
signals having multiple phases.
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